Abrasive article and method of manufacturing the same



Patented er. 3, ltd

NET

at t is Joseph E. dust, Niagara Falls, N. Y., assignor to The Earbodum company,

Niagara Falls,

N. Y., a corporation ei Delaware No Drawing. Application February 241, 1939, Serial No. 258,225

7 (Claims. (6'11. Sli -295) This invention relates to improved abrasive I products and methods of manufacturing the same. More specifically, the invention is concerned with paper-backedeoated abrasives of the character commonly referred. to as sandpaper and employing a protein bond.

While the invention has utility in a variety of products, it is particularly well adapted for the manufacture of coated abrasives of the type com monly referred to as finishing paper. Such products are employed to a great extent in the surfacing of woodwork, such as furniture, where the final surfacing of the wood is given by hand rubbing with the finishing papers.

The finishing papers as heretofore made have been very widely used but are open to a number of objections. In the first place, in order to make the abrasive paper limp and pliable enough so that it can be worked around into corners and curves of small radius, it has been customary to crumple the paper and work it in the hands so as to impart the utmost degree of pliability. When this is done, there is a tendency for the coating on the paper backing to separate from the paper, causing the work to be marred by the detached edge of the coating.

In the second place, in order to improve the pliability and limpness of the paper, it is customary in furniture factories and other similar establishments, to dampen the back of the paper with a wet sponge. -Although this wetting of the paper softens the paper backing itself and improves its pliability, it has two deleterious effects. For one thing, the paper which has been wet is usually scufied up and as a result, the life of the paper is materiallyshortened because the backing rubs away in use and the abrasive paper must be discarded for this reason. In addition, the moisture put onto the paper penetrates the paper and eventually softens the glue adhesive used to attach'the abrasive grains. This occurs in a comparatively short time because finishing papers are almost invariably made on a relatively thin paper backing weighing approximately 40 pounds per paper-makers ream of 480 sheets 24" x 36" and being of the order of 3 to 4 thousandths of an inch thick.

It is accordingly among the objects of the present invention to provide an improved abrasive paper and method of making such product which will not be subject to the objections enumerated above. Another object of the invention is to provide an abrasive paper which will be relatively non-scumng when wet and in which the adhesive used for attaching the abrasive grain is not subjected to special treatments for the purpose of materially softened when the back of the product is moistened with water. Still another object of the invention comprises a coated abrasive product which will be comparatively limp and pliable and in. which the adhesive used for attaching the grains to the backing is tough rather than brittle and relatively water-resistant, and a method of making the same.

In carrying out my invention, 1 firstselect a type of paper which is available on the market under the trade-name Duracel and which contains a larger percentage of alpha cellulose than is present in the usual wood-pulp papers. In preparing such papers, a kraft pulp is selected and reducing the quantity of impurities and providing a pulp containing upwards of alpha cellulose as compared toaround 35% alpha cellulose in the usual kraft paper. Dne way of treat ing the kraft stock to secure such a pulp high in alpha cellulose comprises exposing the pulp to the refining action of a comparatively strong alkaline liquor at about room or slightly elevated temperatures. The specific method of manufacturing such papers are well-mown in the art.

Having preparing a paper web high in alpha cellulose as compared to the usual paper, I next treat the web with a hygroscopic agent and an agent which exerts a tanning action on protein adhesives, such as glue, casein or zein. The two agents are preferably provided in the form of an aqueous solution. The paper may be conveniently treated by passing the web of paper continuously through a vat containing the treating solution, the excess of solution being removed by passage through a pair of pressure rolls in a manner commonly used in the art. The paper is then either passed through a chamber or suspended in a drying atmosphere to remove excess water leaving in the web the usual 5 or 6% of water, the hygroscopic material and the tanning agent distributed through the web. Having thus prepared the backing material, the paper-web is then coated with abrasive grains and protein adhesive in the conventional manner. Such a method comprises, for example, passing the web continuously between a pair of rolls, one of whichis partially immersed in a vat of the adhesive, thus depositing a film of adhesive on one side of the paper web, applyi 1 the abrasive grains to the adhesive film and drying the adhesive. It is also customary in making products of this type to apply a second or sizing coat of the adhesive material by passing the abrasive coated web through a pair of rolls treated paper was found to contain approximate- 1y 6% glycerine, about the same percentage of water, and a small percentage of formaldehyde.

The treatment with the'hygroscopic material. and the tanning agent performs two functions. In the first place, the hygroscopic material which is left in the paper materially softens the paper backing and makes it much more limp and pliable than it is before treatment. In addition, when the glue adhesive is applied for attaching the abrasive grains, the formaldehyde which is present in the paper appears to tan the film of glue adhesive from the paper side and gives a somewhat leathery and tough character to the glue. Such glue is considerably less brittle and has little tendency to peel from the backing when the product is crumpled than is glue not so treated.

In addition, this treatment materially reduces the tendency of the paper to scuif up when it is wet as it does when employed in the usual way. Various other properties of the paper are also markedly changed, as illustrated by the following table showing certain properties of an untreated paper as compared to a paper treated according to my invention.

- Untreated. Treated paper paper While the type of treatment which should be applied to the paper is not critical, it is necessary that the treatment-be kept within a certain range. For example, if too much of the hygroscopic material and the tanning agent are left in the paper, the resulting abrasive product is too limp and pliable for commercial use.

One test which I have found to be well-adapted for determining whether the treatment has provided a satisfactory backing consists in making what is known as an oil absorption test. This test is carried out on a circular sample 1" in diameter cut from the paper and dropped onto the surface of a standard sample of raw linseed oil which is kept for purposes of'this test. The oil is held at 73 F. and the time taken for the paper to become completely saturated with the oil is measured and reported as the oil absorption. Since there is a. slight diflerence in the resultsdepending upon which side of the paper is laid onto the oil, in carrying out the test an equal number of samples are dropped onto the oil surface face down and face up and the average of the results is reported as the measure of oil absorption. v

This test furnishes a convenient measure of the .extent to which the treatment should be carried. Paper for use in my invention should have an oil absorption of less than about and preferably, not less than about 40. I have found, for example, that following the treatment specifically described, the oil absorption of the untreated 40 pound DuraceP' paper was reduced from 256 seconds to around 60 to '70 seconds.

The product of my invention has none of the disadvantages described above in connection with the papers heretofore used. In the first place, it is unnecessary to crumple the abrasive paper to make it limp enough since it has an inherent pliability much greater than that of the ordinary finishing paper. In the second place, although it is usually not necessary to dampen the backing, this canbe done to effect some improvement in limpness without causing the difiiculties resulting when similar treatment is applied to the, ordinary finishing paper.

to leave the sharp edges found in the earlier products.

Finishing papers are commonly made with a garnet abrasive grain but it will be apparent that any type of abrasive material can be employed in the invention. Likewise, while glycerine is a satisfactory hygroscopic material, other hygroscopic materials which are of such a consistency that they can be impregnated into the paper backing, can be substituted. Furthermore, although the invention is particularly well-adapted to finishing papers which, as stated, are commonly made on a 40 pound paper, the invention has been found to have utility in the manufacture of other types of coated abrasives, such as cabinet papers, which are made on paper weighing 70 or 90 pound papermakers cream of 480 sheets 24" x 36". It can also be used to advantage in the manufacture of products using the heavier pound paper commonly employed for belts but sometimes employed for hand-rubbing where relatively severe abrading is to be done. Similarly, the paper web may be prepared from other kinds of cellulose, such as rag stock, provided the alpha cellulose content is high enough to provide satisfactory wet strength and resistance to scufling of the treated web.

While I have described my invention with particular reference to finishing papers and to illustrate the invention have set forth a specific example, it will be apparent that the invention is not restricted to the particular steps or compositions herein described, but may be otherwise practiced within the scope of the appended claims.

I claim:

1. The method of making a water-resistant coated abrasive product which comprises preparing a paper web which is high in alpha cellulose content, treating the web with a hygroscopic material and a tanning agent for a. protein adhesive, and coating the thus-treated web with abrasive grains and a protein adhesive for attaching the grains to the web. 1

2. The method of making a water-resistant 2,224,009 formaldehyde, and coating the thus-treated web with abrasive grains and a protein adhesive for attaching the grains to the web. f

3. The method of making a water-resistant coated abrasive product which comprises preparing a paper web from wood pulp which is high in alpha cellulose content, treating the web with an aqueous solution of glycerine and formaldehyde, drying the treated web to remove the water and leave a web containing glycerine and formaldehyde, and coating the thus-treated web with abrasive grains and a protein adhesive for attaching the grains to the web.

4. The method of making a water-resistant coated abrasive product which comprises preparing a paper web from'wood pulp having an alpha cellulose content of upwards of 90%, wetting the web with an aqueous solution containing approximately 15% glyoerine and 5% formaldehyde, drying the web, and coating it with abrasive grains and a glue bond for attaching the grains to the web.

5. A water-resistant coated abrasive product comprising a paper backing containing upwards of 90% alpha cellulose and from 4% to 7% of glycerine, and a coating of abrasive grains atv tached to the backing. by a film of glue tanned on the paper side to such an extent that it does not soften when the backing ismolstened but not does not soften when the backing is moistened but not tanned throughout sufficiently to be waterproof.

7. A water-resistant coated abrasive characterized by unusual wet-strength limpness and resistance to scumng when wet comprising a paper .backing containing upwards of 90% alpha cellulose and a hygroscopic material, and a layer of abrasive grains attached to the backing by a film of glue tanned on the paper side to such an extent that it does not soften when the backing is moistened but not tanned throughout sufliciently to be waterproof. JOSEPH B. AUST. 

